This invention relates to a document shredder. In particular it concerns a shredder for relatively heavy duty document shredding.
Many document shredders are known which have different characteristics. Essentially a document shredder includes two cutter assemblies which rotate relative to each other, there being overlapping blades or cutting discs on the assemblies which rotate to draw into a nip between the discs the documents to be shredded. In practice a difficulty which arises includes the jamming of the shredder when the documents loaded for shredding are either too numerous or too wide. Occasionally, jamming is caused by foreign objects which enter the nip between the discs. In such situations, it is usually necessary to stop the rotation of the cutter assemblies and, in some cases, reverse the assemblies to remove the foreign objects. Even then difficulties can endure because the foreign object is sometimes jammed between the cutter discs in a manner in which it cannot be easily removed. This can require, at least, partial disassembly
One manner of avoiding jamming of the cutter assembly or of removing foreign objects causing jamming is to provide for the cutting assemblies to be removably spring mounted towards each other. Thus, when a foreign object is jammed in the cutter assembly, the cutter assemblies can be moved apart manually or adjusted under the action of the foreign object attempting to pass between the cutter assemblies. Thereby jamming is avoided. In most cases, this is unsatisfactory since it could cause the foreign object to pass through together with documents in an unshredded form. Also, the possibility arises that operators will be tempted to put their hands close to the cutter assemblies, and this is potentially dangerous.
A different problem which arises with shredders is to provide for efficient operation for heavy duty shredders, namely shredders able to digest documents of about 20 inches width. The shredding requirement is to simultaneously shred documents into fine strips of about 1/38" width by 3/8" in length. A demand exists for heavy duty shredders having a wide mouth and cutter assembly to receive documents in the order of 20 inches, and yet be easily operable with an efficient drive.
One form of drive motor which is efficient and which operates under low power conditions would be a single phase electric motor. The problem, however, is that with a cutter assembly of about 18 inches or more, the power requirement for a shredder would normally require a three-phase motor which is relatively less energy efficient, and requires special wiring There is accordingly a need to provide for an efficient low power drive motor means, whereby power from a single phase motor can be transmitted to operate the cutter assemblY efficiently when the assembly is wide mouthed.
There is accordingly a need to provide a document shredder for high volume heavy duty operation under low power efficient conditions while avoiding the problems of jamming.